The taking of blood from a subject for treatment and returning the blood to the subject requires control of a relatively large number of variables. Some of these are so critical that failure to control them adequately can result in death of the patient. As one of the simplest examples, the blood returning to the patient must be free of air bubbles. As another example, if the rate at which blood is being taken from the patient is such that there is an inadequate circulating blood volume, cardiovascular shock and death can result. Monitoring the patient's pulse rate and blood pressure, for example, allows anticipation of undesirable changes and the taking of appropriate compensating actions.
As aforenoted, the number of variables which must be monitored is such that extracorporeal treatment of blood, as exemplified by dialysis, has been almost prohibitively expensive. Much effort has already been expended in the attempt to decrease the cost of necessary equipment. The amount of supervision by technical personnel required, however, remains a major obstacle to utilization of this life-saving technique. This cost is principally due to the necessity for expert monitoring of the patient's condition. Also, the necessity of avoiding the dangers involved in passing blood from one patient through a system through which blood from another patient has passed, requires extensive cleaning procedures for contaminated hardware, and use of disposable equipment, again involving considerable expenditure of time by skilled personnel to perform the necessary steps preparatory to performing the procedure itself. For these reasons the need for automated, economical equipment is great. Moreover, the number of individuals capable of benefitting from extracorporeal treatments of blood is so great that not all can receive the required treatment unless suitable automatic equipment can be developed. Such equipment, preferably, should be automated to the point where self-treatment or markedly increased efficiency of existing treatment facilities and personnel can be anticipated.
It is recognized that the ultimate monitor must be human; the condition of the patient can vary so widely and in so many ways while under treatment that the judgment of skilled personnel must be available. However, once a set of conditions is selected within which the patient's condition and the patient's blood must be maintained, the task of determining whether the conditions are met can be turned over to a machine. Such a machine must be able to discriminate between a temporary deviation from set conditions, and must be able to apply corrective measures designed to bring said conditions within preselected limits. However, it is essential that when any significant variable deviates beyond preselected limits and when the corrective measures applied by the machine fail to bring said variable back to the appropriate range, the machine must then halt the circulation of blood for the protection of the patient and preferably should activate an alarm.
In view of the large number of individuals known to require treatment for such pathological conditions as uremia, and the potential for use of extracorporeal treatments of blood in other conditions, such as hypoxemia, intoxication and poisoning, there is a pressing need for improved treatment systems at substantially reduced cost per patient. Conventional apparatuses fail to meet these requirements.